This invention relates to a modification of the lapidary industry's traditional jamb peg faceting mechanism. For grinding facets with a traditional jamb peg, a gemstone is normally adhesively attached to one end of a relatively short metal or wooden dowel-like peg (sometimes also referred to as a "quill" or "dop stick") with the rear tip of the peg jambed or positioned into a backplate assembly whose surface is provided with various holes or slots. The vertical location of the various backplate holes or slots into which the dop stick is fitted establishes an approximate triangle which permits engagement by the stone to an horizontally rotating abrasive lap wheel with the said assembly providing the three necessary elements required for faceting: 1, controlling freehand rotation about the dop stick's longitudinal axis (INDEX); 2, controlling movement about an axis extending perpendicular to the dop stick's axis of rotation (ANGLE); 3, controlling the dop stick in an elevation vertically addressed to the fixed angle position of the abrasive disk (HEIGHT). Consequently, with few mechanical stops or controls in a standard jamb peg device great emphasis must be placed on the operator's experience and ability to estimate and establish the peg or dop stick setting to achieve coordinated discipline of height, index, and angle of the stone relative to the rotating abrasive disks for each facet and/or row or tier of facets which comprise the plurality of facets intended to be placed on the stone in the desired symmetry and configuration.
With more contemporaneous protractor type faceting machines as well as jamb peg faceting machines, a rough crystal is faceted in a two-phase operation: in the first phase, the crystal is adhesively attached to a dopstick and the top (called the "crown") or the bottom (called the "pavilion") is cut. The dopstick/stone assembly is then removed from the faceting machine so a second dopstick may be adhesively attached to the cut half of the crystal in a precisely opposite orientation; in the second phase, the initial dopstick is removed and the new dopstick/stone assembly is then returned to the faceting machine so the remaining half of the crystal may be completed.
Over the years, various innovations have been introduced to the jamb peg assembly so as to provide greater mechanical discipline as an alternative to such excessive dependance on operator judgment for height, angle and index. While the level of the art has been improved, none of these variations in industry literature or patents have provided comprehensive and calibrated coordination of height, angle and index together with automatic and rigidly disciplined angle and height positions which remain independent of the operator's judgement.
This invention is a calibrated jamb peg because it provides such coordinated angle plus height and index calibration by defining machine elements as the three elements of a right triangle: 1, the two-part quill member length functions as the hypotenuse; 2, the vertical positions of the multiple backplate grooves function as the opposite side, 3, and the distance between the rear of each groove and the position on the rotating abrasive lap wheel of the lowest end of the quill member functions as the adjacent side. By providing a mathematically correct vertical groove position for each angle, the operator need confirm only the first angle setting and all other angle grooves will thus be mathematically appropriate. Any minor discrepancy introduced by variable stone size can be accommodated by using a template to confirm the proper height and angle of the specific groove.